NEW YORK, Dec 18 (Reuters) - Rates banks charge each other for U.S. dollar-denominated funds slid to fresh 4-1/2 year lows on Thursday in the wake of the U.S. Federal Reserve's move this week to keep interest rates at rockbottom levels for a sustained period.

The Fed's dramatic measure that sent its target rate to a record low range of zero to 0.25 percent has helped to unlock credits for cash-strapped borrowers, but it has not been the immediate jolt that some traders had hoped.